1. Technological Field
The present disclosure relates generally to the field of multimedia processing. More particularly, the present disclosure is directed to precisely synchronizing media processing within a wireless network.
2. Description of Related Technology
As is well known within the electronic circuit design arts, high speed integrated circuit (IC) design typically requires consistent and accurate distribution of a time reference. Specifically, an accurate time reference is required to, inter alia, ensure that data is processed correctly and consistently throughout the integrated circuit. Media processing is one specific area of the processing arts where timing problems can result in performance issues that are easily perceptible to humans. For example, audio playback with a glitchy or irregular clock can result in audible artifacts and distortions. Similarly, video playback with poor quality clocks may result in visible freezing, “chunking”, etc. Typically, video errors on the order of a few milliseconds can be perceived whereas audio errors can be perceived within a few microseconds (the human ear is more sensitive to anomalies).
For example, consider two or more wireless audio devices that are configured to provide a “stereo” and/or “surround” audio experience. If the wireless audio devices are not correctly synchronized, then the audio playback for one speaker will be slightly offset in time from the other speaker(s). Since the human brain interprets perceived volume differences and time differences as being caused by the virtual location of sound sources relative to the human, the slight offset in time will be interpreted as an incorrectly reproduced stereo image. Specifically, the resulting “inter-temporal distortion” will be perceived as a stereo image that is not centered, but is off to one side. The human brain can detect time differences as small as 10 microseconds (e.g., typically half an audio sample).
Wireless networks must robustly handle changing radio environments, unknown propagation delays, etc. Generally, wireless devices utilize an internal free-running oscillator to generate internal clocking. Due to manufacturing variance and tolerances in oscillator components, wireless networks must also assume that each device has an imperfect time reference. For this reason, a myriad of synchronization schemes and standards for synchronizing time between wireless devices have been developed. Typical solutions for network synchronization regularly provide time information across the wireless network; each device of the network determines an appropriate adjustment to its local free-running clock. Existing wireless synchronization techniques are accurate to only within a few milliseconds (which is magnitudes greater than the human brain's audio acuity).
Moreover, even though wireless systems can synchronize their internal clocks to a common time reference for modem operation, typical media processing is performed via a separate processor (e.g., an application processor). Accordingly, distortion-free media playback also requires that the media sub-system can receive a high quality time reference from the modem chip.